The first issue is that your father has a legal interest in the estate, but is not in a position to give expression to it due to dementia. You do not have any legal standing. If you need that to be sorted out, you need to involve your own solicitor: you are entering difficult territory, not suitable for non-specialists.
I presume that your uncle who is the administrator is not suffering from dementia. He has an equal duty to both beneficiaries, and has no right to do anything which benefits himself (and through him, his son) more than it benefits your father. You believe that may be happening. That concern should be communicated to the solicitor dealing with the estate, preferably by a solicitor acting in your father's interest.
You also believe that the administrator's son is meddling in the administration. That concern should also be communicated to the solicitor dealing with the estate.
In general, where the beneficiaries can not agree on a sale or transfer of land, the preferred practice is to go to market by way of auction.